1. Field of the Invention
The present invention relates generally to a fuel cell system, and in particularly to a fuel cell system comprising an air cooling device for improving performance thereof.
2. Description of the Prior Art
Fuel cell power system is capable of generating electrical power energy by means of electro-chemical reaction between a fuel, such as hydrogen and methanol, and an oxidizer, such as oxygen. Based on the electrolyte thereof, the fuel cell is classified as proton exchange membrane fuel cell or polymer electrolyte membrane fuel cell, abbreviated as PEMFC or PEM, alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC).
Among these known fuel cells, the PEMFEC is the best-developed technique, having the advantages of low operation temperature, fast start-up and high power density. Thus, the PEMFC is very suitable for transportation vehicles and power generation systems, such as home power systems and other portable and stationary power generation systems.
Fuel cell of power smaller than 1 kilo-watt usually comprises an air cooling device. FIG. 1 of the attached drawings shows an example of conventional power fuel cell systems comprising a fuel cell stack 102. Air containing oxygen is drawn in by an air pump 104, and hydrogen stored in a hydrogen canister 110 is conveyed through a solenoid valve 106 and a pressure regulator 108 to the fuel cell stack 102. The electrochemical reaction between the hydrogen and oxygen generates electricity with water and heat as byproducts of the reaction. The heat generated subsequently causes the rise of a temperature of the fuel cell stack 102. When the temperature of the fuel cell stack 102 rises too high, a cooling fan 112 is driven to turn on for cooling.
FIG. 2 shows a perspective view of a conventional fuel cell comprises a cooling fan. The fuel cell stack 102 includes a plurality of fuel cell units 202, each of which comprises an anode plate, a cathode plate, a membrane electrode assembly (MEA), and two gas diffusion layers at the two sides of MEA. Two adjacent cell units 202 sandwich a cooling plate 204 which comprises a plurality of parallelly arranged air grooves 206. When the fuel cell stack 102 reaches a high temperature, the cooling fan 112 is driven to turn on and cooling air is drawn into the grooves 206. The cooling air absorbs and carries away the heat inside the fuel cell stack 102. Subsequently, the temperature of fuel cell stack 102 is decreased.
The electro-chemical reaction between hydrogen and oxygen is highly improved in suitable moisturized condition. Accordingly, the temperature of the fuel cell stack 102 should be maintained at below 40˜60° C., otherwise, there may be insufficient water and reaction rate is low. Therefore, when the fuel cell stack reaches a temperature higher than 40˜60° C., the cooling fan 112 is driven to turn on for cooling. However, the cooling fan 112 can only generate cooling air of low pressure and velocity, and the cooling effect is poor. Therefore, the fuel cell stack 102 is not capable to work at heavy load and provide large working current. Moreover, an extra space is required for the placement of the cooling fan 112.
Furthermore, to promote the electrochemical reaction between oxygen and hydrogen, a solenoid valve 106 and a pressure regulator 108 control the flowing of hydrogen to the fuel cell stack 102. Such a regulation limits the utility of hydrogen.
It is thus desired to provide a fuel cell system that overcomes the above-discussed disadvantages of the prior art. The present invention provides a fuel cell system with an air cooling device, which enables the fuel cell stack to work at higher temperature while it does not require a cooling fan for cooling.